As a display device for use in electronic office equipment such as a word processor, a notebook personal computer or a monitor for a personal computer, a mobile terminal or a TV set, CRT (cathode ray tube) has mainly been used. In recent years, liquid crystal display devices have been popularly used taking the place of CRT due to their thin thickness, light weight and small electric power required. The liquid crystal display device contains a liquid crystal cell and a polarizing plate. The polarizing plate usually comprises a protective film and a polarizing film and is obtained by dyeing a polarizing film comprising a polyvinyl alcohol film with iodine, stretching the dyed film and laminating a protective film on each side of the stretched film. With a transmission type liquid crystal display device, this polarizing plate is disposed on both sides of a liquid crystal cell and, in some cases, one or more optically-compensatory sheets are disposed thereon. Also, with a reflection type liquid crystal display device, a reflection plate, a liquid crystal cell, one or more optically-compensatory sheets and a polarizing plate are usually disposed in this order. The liquid crystal cell usually comprises liquid crystal molecules, two sheets of substrates for sealing the molecules and an electrode layer for applying an electric voltage to the liquid crystal molecules. The liquid crystal cell performs ON-OFF display based on difference of alignment state of the liquid crystal molecules and can be applied to any of transmission type, reflection type and semi-transmission type liquid crystal display devices. There have been proposed display modes such as TN (Twisted Nematic) mode, IPS (In-Plane Switching) mode, OCB (Optically Compensatory Bend) mode, VA (Vertically Aligned) mode, ECB (Electrically Controlled Birefringence) mode and STNJ (Super Twisted Nematic) mode.
An optically-compensatory sheet is used in various liquid crystal display devices for the purpose of avoiding coloration of image and enlarging the viewing angle. As the optically-compensatory sheet, there have conventionally been used a stretched birefringent polymer film. It has been proposed to use, in place of the optically-compensatory sheet comprising a stretched birefringent film, an optically-compensatory sheet having an optically anisotropic layer formed on a transparent support from a low molecular or high molecular liquid crystalline compound. Since liquid crystalline compounds can be in various alignments, use of the liquid crystalline compound has enabled one to realize optical properties that can not be provided by the conventional stretched birefringent polymer films. Further, such optically-compensatory sheet can also function as a protective film for a polarizing plate.
Optical properties of the optically-compensatory sheet are determined by optical properties of a liquid crystal cell, specifically, depending upon the difference in display mode. Use of the liquid crystalline compounds enables one to produce optically-compensatory sheets having various optical properties corresponding to various display modes. Optically-compensatory sheets using liquid crystalline compounds corresponding to various display modes have already been proposed. For example, an optically-compensatory sheet which can be used for an ECB-mode liquid crystal cell performs such optical compensation that, when a voltage is applied, liquid crystal molecules are in an alignment of being inclined with respect to the substrate plane with dissolving the hybrid structure, thus improving viewing properties with respect to contrast by preventing leakage of light in the oblique direction upon black display.
Thus, with the ECB-mode liquid crystal display devices, viewing angle properties have been improved. With conventional liquid crystal display devices, however, a problem has not yet been solved that polarizing plates suffer shrinkage when used in a severe environment, for example, a high-temperature or high-humidity environment and, as a result, leakage of light is caused.
Such leakage of light is caused by shrinkage of the polarizing plate, and there is an example that the leakage of light can be decreased by selecting materials of an adhesive for the polarizing plate (see JP-T-2004-516359 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)).